The present invention relates to a deflection yoke and a cathode ray tube, more particularly to a deflection yoke adapted for use in a color cathode ray tube, and also to a color cathode ray tube using such a deflection yoke.
Three electron beams in a color cathode ray tube are deflected by a deflection yoke for scanning a fluorescent screen to form rasters.
The deflection yoke consists of a horizontal deflection coil, a vertical deflection coil, an annular core and so forth.
When a horizontal deflection current is supplied to flow in the horizontal deflection coil, a horizontal deflection magnetic field is generated to deflect electron beams for horizontal scanning.
Similarly, when a vertical deflection current is supplied to flow in the vertical deflection coil, a vertical deflection magnetic field is generated to deflect electron beams for vertical scanning.
Most color cathode ray tubes having an inline-type electron gun are generally used such that the center beam, out of the entire three electron beams therein, is used for displaying green, while the two side beams are used for displaying red and blue respectively.
In such a cathode ray tube, there occurs misconvergence of a specific pattern when the mutual positional relationship between the electron beams and the vertical deflection magnetic field is deviated horizontally either leftward or rightward.
For example, if an electron gun in a cathode ray tube is installed with a rightward deviation in regard to the center axis of the cathode ray tube, the electron beams are also deviated rightward, as shown in FIG. 1A.
Meanwhile, if a deflection yoke is installed with a leftward deviation in regard to the center axis of the cathode ray tube, the vertical deflection magnetic field is also deviated leftward, as shown in FIG. 1B.
That is, in the cases shown in FIGS. 1A and 1B, the electron beams are deviated rightward in regard to the vertical deflection magnetic field.
In such a case, as shown in FIG. 2, there occurs, due to the vertical deflection, misconvergence of a pattern where red and blue rasters are deviated inward or outward from a green raster in each of upper and lower peripheral areas of a screen.
The misconvergence of this pattern is derived from the lateral asymmetrical relationship between the positions of the vertical deflection magnetic field and the electron beams. Hereinafter, it will be referred to as "misconvergence derived from lateral asymmetry"; and, the misconvergence of this pattern will be termed TLV in the description below.
For correction of such TLV, generally the following methods have been known in the related art.
The first method is carried out by employing a magnetic member. More specifically, a magnetic member is attached to either the left or the right side of the rear end of the deflection yoke, and the misconvergence TLV is corrected by laterally unbalancing the vertical-deflection magnetic field.
And the second method is carried out by employing a pair of coma-aberration correcting coils which are disposed on both left and right sides of the deflection yoke and in which vertical deflection currents are supplied to flow. More specifically, the misconvergence TLV is corrected by changing the currents that are flowing in the left and right correcting coils, thereby laterally unbalancing the magnetic field generated.
Any of the known correction methods described above is capable of executing proper correction of the misconvergence TLV, hence achieving satisfactory convergence characteristics with respect to the TLV.
However, none of the above methods is adequate to perform sole correction of the TLV alone. That is, according to the first method, the magnetic member absorbs not only the vertical deflection field but also the horizontal deflection field generated by the horizontal deflection coil. Consequently, asymmetry of the horizontal deflection magnetic field is induced as an incidental harmful effect. And this asymmetry causes other misconvergences of various patterns as well. Since the first method executes the desired correction by utilizing a leakage magnetic flux generated from the deflection yoke, it is unavoidable that the amount of the correctable TLV is somewhat limited.
Meanwhile, according to the second method, the magnetic field generated from the coma-aberration correcting coil becomes more asymmmetric in proportion to an increase of the TLV correction amount. Therefore, the symmetry for correcting the coma aberration is disordered to eventually generate misconvergences of various patterns.
Thus, it is impossible to attain improvements by adopting the first or second methods mentioned, and the convergence characteristics of any pattern, other than the TLV, are harmfully affected and rendered worse.